1. Field of the Invention
The disclosed and claimed concept relates to circuit interrupters and, more specifically, to vacuum circuit interrupters, such as, for example, a vacuum circuit interrupter including electrodes enclosing heat transfer assemblies.
2. Background Information
Circuit breakers and other such devices provide protection for electrical systems from electrical fault conditions such as current overloads, short circuits, and low level voltage conditions. In one embodiment, circuit breakers include a spring-powered operating mechanism which opens electrical contacts to interrupt the current through the conductors in an electrical system in response to abnormal conditions. In particular, vacuum circuit interrupters include separable main contacts disposed within an insulated and hermetically sealed vacuum chamber within a housing. The contacts are part of an electrode including a stem and a contact member. Generally, one of the electrodes is fixed relative to the housing. The other electrode is moveable relative to the housing and the other electrode. In a vacuum circuit interrupter, the moveable electrode assembly usually comprises a copper stem of circular cross-section having the contact member at one end enclosed within the vacuum chamber, and a driving mechanism at the other end which is external to the vacuum chamber.
Vacuum interrupters are, in one embodiment, used to interrupt medium voltage alternating current (AC) currents and, also, high voltage AC currents of several thousands of amperes or more. In one embodiment, one vacuum interrupter is provided for each phase of a multi-phase circuit and the vacuum interrupters for the several phases are actuated simultaneously by a common operating mechanism, or separately or independently by separate operating mechanisms. The electrodes can take three positions: closed, opened and grounded.
When the electrodes are in the closed position, the contact members are in electrical communication and electricity flows therethrough. In this configuration, the electrodes become heated, Generally, the amount of heat generated is a function of the cross-sectional area of the electrodes and the amount of current. That is, smaller electrodes and/or higher currents generate more heat. Accordingly, using traditional electrodes, in order to have a circuit breaker rated at a higher current, the electrode must be larger.
Larger electrodes, however, have several disadvantages. For example, larger electrodes are more expensive and require a more robust operating mechanism, which is also more expensive. Further, a larger/more robust operating mechanism requires more energy to operate and is, therefore, more expensive to use as well. There is, therefore, a need for an electrode that is rated at a higher current while having a smaller size and/or volume. There is a further need for such an electrode to be operable with existing circuit breakers.